Guidance for Federal Land Management in the … for Federal Land Management in the Chesapeake Bay...
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EPA841-R-10-002 May 12, 2010
Guidance for Federal Land Management
in the Chesapeake Bay Watershed
Chapter 6. Decentralized Wastewater Treatment Systems
Nonpoint Source Pollution Office of Wetlands, Oceans, and Watersheds
U.S. Environmental Protection Agency
Guidance for Federal Land Management in the Chesapeake Bay Watershed
Chapter 6. Decentralized Wastewater Treatment Systems 6‐1
Chapter 6.
Decentralized Wastewater Treatment
Systems 6.
Contents
1 Nitrogen-Reduction Implementation Measures....................................................................6-3
2 Introduction and Background ...............................................................................................6-6
3 Nutrient-Reduction Processes for the Decentralized Wastewater Sector............................6-9
3.1 Nitrogen.......................................................................................................................6-9
3.2 Nitrogen Pretreatment .................................................................................................6-9
3.3 Phosphorus ...............................................................................................................6-10
3.4 Permeable Reactive Barriers ....................................................................................6-11
3.5 System Configuration................................................................................................6-12
4 Treatment Technologies and Costs ...................................................................................6-13
4.1 Conventional Systems...............................................................................................6-15
4.2 Land/Vegetative Treatment Systems ........................................................................6-15
4.3 Suspended Growth Systems.....................................................................................6-15
4.4 Attached Growth Aerobic Systems............................................................................6-16
4.5 Add-On Anoxic Filters with a Carbon Source............................................................6-17
4.6 Composting Toilet Systems.......................................................................................6-18
4.7 Cluster Treatment Systems.......................................................................................6-19
4.8 Soil Dispersal Systems..............................................................................................6-19
4.9 Effluent Reuse...........................................................................................................6-20
5 Wastewater Planning and Treatment System Management..............................................6-23
5.1 Public Education and Involvement ............................................................................6-23
5.2 Planning ....................................................................................................................6-24
5.3 Performance Requirements ......................................................................................6-24
5.4 Recordkeeping, Inventories, and Reporting ..............................................................6-25
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5.5 Financial Assistance and Funding.............................................................................6-25
5.6 Site Evaluation ..........................................................................................................6-25
5.7 System Design ..........................................................................................................6-26
5.8 Construction/Installation ............................................................................................6-26
5.9 Operation and Maintenance......................................................................................6-27
5.10 Residuals Management.............................................................................................6-27
5.11 Training and Certification/Licensing ..........................................................................6-27
5.12 Inspections and Monitoring .......................................................................................6-28
5.13 Corrective Actions and Enforcement.........................................................................6-28
6 References.........................................................................................................................6-30
Guidance for Federal Land Management in the Chesapeake Bay Watershed
1 Nitrogen-Reduction Implementation Measures The U.S. Environmental Protection Agency (EPA) recommends protecting surface waters in the
Chesapeake Bay watershed from nitrogen (N) discharged by decentralized wastewater
treatment systems by using N-reduction technologies and enhanced system management.
Implementation Measures: D‐1. Specify the following risk‐based, N‐removal performance levels for all new
and replacement individual and cluster systems:
20 milligrams per liter (mg/L) total nitrogen (TN) standard* for all new
subdivisions and commercial and institutional developments and all
system replacements throughout the Chesapeake Bay watershed.
10 mg/L TN standard* for all new developments and all system
replacements in sensitive areas—i.e., between 200 and 1,000 feet of the
ordinary high water mark of all surface waters, or between 200 and
500 feet of an open‐channel MS4.
5 mg/L TN standard* for all new developments and system replacements
in more sensitive areas—i.e., between 100 and 200 feet of the ordinary
high water mark of all surface waters, or between 100 and 200 feet of an
open‐channel MS4.
100‐foot setback from surface waters and open channel MS4s for all
effluent dispersal system components.
* Effluent standards can be met by either system design or
performance, as verified by third‐party design review or field
verification. Except in sandy or loamy sand soils, a 5 mg/L N
reduction credit is given when using time‐dosed, pressurized
effluent dispersal within 1 foot of the ground surface and
more than 1.5 feet above a limiting soil/bedrock condition.
D‐2. Ensure wastewater treatment performance effectiveness and cost efficiency
by using cluster systems with advanced N‐removal technology sufficient to
meet the standards specified above for all newly developed communities
and densely populated areas.
D‐3. Sustain treatment system performance in perpetuity through management
contracts with trained and certified operators for all advanced N‐removal
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systems, and responsible management entity (RME) operation and
maintenance (O&M) for all cluster and nonresidential systems. RMEs
include sanitation districts, special districts, and other public or private
entities with the technical, managerial, and financial capacity to assure long‐
term system performance.
D‐4. Preserve long‐term treatment system performance with management
practices designed to protect system investments, by doing the following:
Conducting GIS‐based inventories of all individual and cluster
(i.e., decentralized) wastewater systems in all areas that drain into the
Chesapeake Bay or its tributaries. Inventory information includes system
location (i.e., latitude/longitude), type, capacity, installation date, owner,
and relevant information on complaints, service (including tank pump‐
out), repairs, inspections, and dates. Inventory data is stored
electronically in a format amenable for use in watershed studies, system
impacts analyses, and supporting general management tasks. EPA offers
The Wastewater Information System Tool (TWIST) (USEPA 2006) as a free
resource for managing that information in a user‐friendly database.
Health departments, state agencies, RMEs and others can adapt, amend,
or otherwise modify TWIST without restriction or obligation.
Requiring inspections for all systems on a schedule according to
wastewater type, system size, complexity, location, and relative
environmental risk. At a minimum, qualified inspectors inspect all
systems at least once every 5 years and inspect existing systems within
sensitive areas at least once every 3 years. Inspect advanced treatment
systems, cluster systems, and those serving commercial, institutional, or
industrial facilities at least semiannually and manage such systems under
an O&M agreement or by an RME. Inspections are consistent with EPA
management guidelines for individual and cluster systems. A service
professional or other trained personnel conducts routine monitoring of
all systems, and periodic effluent sampling for cluster and nonresidential
systems, on the basis of system type, operating history, manufacturer’s
recommendations, and other relevant factors.
Repairing or replacing all malfunctioning systems when discovered, with
new or replacement technologies capable of meeting the N‐removal
standards specified above.
Requiring reserve areas for installing a replacement soil dispersal system
that is equal to at least 100 percent of the size of the original effluent
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dispersal area. Treatment systems using effluent time‐dosing (i.e., not
demand‐dosing) to the soil can have reserve areas equal to at least
75 percent of the total required drainfield area. Systems with pressurized
drip effluent dosing or shallow pressurized effluent dispersal and those
with dual drainfields operated on active/rest cycles (i.e., alternating
drainfields) can have reserve areas equal to at least 50 percent of the
original required dispersal area.
D‐5. Remove nitrate in subsurface effluent plumes that enter surface waters by
using effective, low‐cost technologies such as permeable reactive barriers
(PRBs). PRBs are low‐cost, pH‐controlled trenches filled with sand and a
degradable carbon source, such as sawdust, shredded newspaper, or wood
chips, designed to intercept groundwater plumes and reduce the TN
concentration via denitrification.
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2 Introduction and Background Individual on-site and cluster (decentralized) wastewater systems treat household and
commercial wastes in suburban, exurban, and rural areas throughout the Chesapeake Bay
watershed. The Chesapeake Bay Program (USEPA 2009) estimates that about 25 percent of
the homes in the watershed—2.3 million total—rely on these systems, which disperse treated
effluent to the soil. EPA predicts that decentralized system installations will increase over the
next 20 years by about 35 percent (i.e., 800,000 new systems), eventually reaching 3.1 million
(USEPA 2009).
Nearly all the solids and phosphorus (P) discharged from decentralized wastewater systems are
retained by the soil, through physical filtration, adsorption, and precipitation processes
(USEPA 2004), although release of P into the environment is a concern in sandy soils under
certain conditions, especially with poor vertical separation distance with groundwater (Bussey
1996). However, N in wastewater is ultimately converted to nitrate upon infiltration into aerobic
soils, a stable, soluble, and highly mobile form of this nutrient that negatively affects
groundwater and surface water quality. For those reasons, in this guidance EPA focuses on
implementation measures to reduce N.
Decentralized wastewater systems contribute approximately 12.5 million pounds of N to the
Chesapeake Bay annually, or about 4.5 percent of the total load. According to current
Chesapeake Bay nutrient loading models, most of the N load from such systems—about
60 percent—comes from the Potomac and Susquehanna river drainage areas within
Pennsylvania, Virginia, and Maryland. With 800,000 new systems predicted over the next
15 years, significant reductions in N loads from new and existing systems are needed.
The Chesapeake Bay nutrient and sediment reduction goals include decreases in current and
future pollutant loads from decentralized treatment systems. A new generation of “hardware and
software”—treatment technologies and management practices—are needed to achieve the
reductions. This section describes those technologies, management practices, and associated
implementation measures. Implementation measures for achieving the reductions include
installing treatment units with optimal N-removal capabilities in sensitive areas near surface
waters; using standard N-removal systems in other areas; and ensuring that all treatment
systems are appropriately operated, maintained, and managed. The measures encompass a
range of treatment technologies, planning and performance considerations, and management
actions needed to address N export from decentralized systems.
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The implementation measures described in this chapter support two primary goals for
addressing N inputs to the Chesapeake Bay from these systems:
Prevent further impairment of the Chesapeake Bay by significantly reducing N levels in
wastewater from new residential, commercial, and institutional developments using
decentralized systems
Reduce N inputs to the Chesapeake Bay from existing individual and cluster wastewater
systems by replacing malfunctioning systems with better-performing technologies and by
managing all systems to ensure long term performance
Implementation measures to achieve those goals include repairing or replacing malfunctioning
systems, targeting high-risk systems in sensitive areas for replacement with advanced treatment
units, clustering replacement systems where possible to implement better-performing and more
efficient community treatment facilities, inspecting all systems throughout the Chesapeake Bay
watershed, and installing PRBs where technically and economically feasible to reduce N
concentrations in targeted effluent plumes. Those approaches are based on more than
2 decades of research and field studies on decentralized system applications.
Key findings on system performance, effects on groundwater, and the opportunities presented
by next-generation treatment technologies are summarized in the Final Report for the La Pine
National Decentralized Wastewater Treatment Demonstration Project (Rich 2005), a joint effort
of EPA and other federal, state, and local agencies:
The groundwater investigations have found significant existing nitrogen pollution
and the 3-D model has predicted extensive future contamination of the aquifer.
The model also predicted, based on the field performance of denitrifying systems
in the project, that contamination could be slowed or stopped using onsite
wastewater treatment technologies, and that, as the region is retrofitted with
denitrifying technologies, the existing contamination would be flushed from the
groundwater system via existing natural discharge points.
The field test program, in addition to identifying systems that can remove a large
proportion of the nitrogen in residential wastewater, found that conventional
systems are not protecting the aquifer from nitrate contamination. Conventional
systems that were previously thought to denitrify up to 50% of the nitrate
discharged from septic tanks were found to achieve significantly less
denitrification when process and environmental variables were accounted for.
The La Pine Project, EPA’s Environmental Technology Verification (ETV) program, the National
Sanitation Foundation standards program, and other research efforts across the country have
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identified and tested a number of denitrifying wastewater systems and found that performance
varies considerably. However, some systems do perform optimally in removing TN from the
effluent—e.g., to concentrations lower than 5 mg/L—and others are capable of N effluent levels
in the 10 and 20 mg/L range.
Higher treatment performance levels are needed in sensitive areas to protect or restore surface
water quality. Research and field studies confirm that effluent plumes with elevated nitrate levels
move laterally over long distances—i.e., greater than 300 feet in unconfined, sandy aquifers
(Walker et al. 1972; Robertson and Cherry 1992). N concentrations in effluent plumes are
affected by soil oxygen levels, soil composition, plant uptake, labile carbon content, travel
distance, rate of movement, mixing, and other factors. The measures specified in this chapter
include descriptions of treatment and dispersal systems that can meet the performance
standards needed to protect the Chesapeake Bay and its tributaries and include more stringent
treatment levels in sensitive areas near waterbodies. Such measures are consistent with efforts
in the states that have already been adopting treatment zone setbacks and treatment standards
to address N and other pollutants in coastal areas (Joubert et al. 2003).
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3 Nutrient-Reduction Processes for the Decentralized Wastewater Sector
Nutrients—primarily P and N—are usually present in significant levels in domestic and
commercial wastewater. Nutrient treatment and removal involve processes that occur either in
treatment system components or in the receiving environment, as summarized below.
3.1 Nitrogen N is the primary pollutant of concern along the coastal areas of the eastern United States,
including the Chesapeake Bay. N discharges are a concern both as a drinking water
contaminant (nitrate) and as an aquatic plant nutrient, particularly in N-sensitive surface waters
and nearshore marine waters. N is not readily or consistently removed in conventional individual
and cluster soil-based systems because conventional soil-discharging systems are not designed
to remove N, and most soils have a limited capacity to retain or remove N. Organic N in
wastewater is generally converted to ammonium N in the septic tank. Ammonium N is quickly
nitrified as the wastewater infiltrates the aerobic soil. Nitrate-N is stable, soluble, and highly
mobile in the subsurface environment. Biological denitrification of the nitrate is usually limited
because the soil is often aerobic near the ground surface and usually has very little organic
carbon, which is required by heterotrophic denitrifying microorganisms. Therefore, where N
removal is required for dispersal, pretreatment that achieves both nitrification and denitrification
is usually necessary before the wastewater is dispersed to the soil.
3.2 Nitrogen Pretreatment Many reasonably priced natural and mechanical pretreatment systems, specifically designed for
individual and cluster systems, are available today. The most popular example of such systems
is the recirculating media filter, with timed pressure-dosing effluent dispersal. The filter media is
typically sand, gravel, textile, or peat. A portion of the filtered effluent is recycled back to the
septic tank (or pump/recirculating tank) and filter several times before discharge. Denitrification
is supported by the low-oxygen, high-carbon environment that exists in the recirculating tank.
The systems are able to consistently remove an average of 50 percent or more of the TN in the
septic tank effluent—reducing the TN from a typical influent range of 40–50 mg/L for single
family homes to 15–20 mg/L (Otis 2007; USEPA 2002a; Jenssen and Siegrist 1990; Higgins et
al. 2002; Smith et al. 2008; Rich et al. 2003).
To achieve TN levels of 3–5 mg/L and lower, an additional denitrifying unit process is usually
installed to augment the pretreatment system. To sustain a denitrification process capable of
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high levels of N removal, the nitrified effluent from the pretreatment process must be exposed to
a reactive carbon source in a low-oxygen environment before discharge. For larger installations,
methanol, acetic acid, molasses, or other organic chemicals are added to the anaerobic reactor.
However, the cost of building, operating, and maintaining an external chemical feeding system,
coupled with the cost of chemicals, power for a feed pump, controls, and chemical storage
increase N-removal expenses substantially.
Carbon sources are not equal in terms of O&M requirements. For example, methanol is very
sensitive to under- or over-dosing, and thus requires special attention to ensure that the system
is monitored enough to control dosing for optimal N-removal and biochemical oxygen demand
control. By contrast, sawdust and newspapers need to be replaced only when effluent N breaks
through (i.e., the denitrification capacity of the sawdust or newspaper has been exhausted).
Proprietary denitrifying units, which avoid the need for additional feed pumps, controls, and
chemicals, are now available. Such units include a slowly degradable organic material in the
reactor tank that can last several years. Field testing has documented TN effluent
concentrations of 3–5 mg/L and even lower (Smith et al. 2008; Lombardo et al. 2005).
Further N removal occurs in the soil, particularly when pretreated effluent is dispersed uniformly
via alternating dose/rest cycles. Plant uptake of N, soil oxygen levels, carbon sources,
temperature, and residence time are key factors in N-removal levels during this final stage of
treatment, which are estimated in the 50 percent reduction range (Long 1995; Otis 2007).
Additionally, some soils contain sufficient labile carbon to denitrify effluents regardless of the
method of dispersal (Anderson 1998; Gold et al. 2002; Starr and Gillham 1986; Bushman 1996;
Hiscock et al. 1991). Other important variables could include seasonal use (Postma 1992),
in-stream processes, including the matrix through which the groundwater enters nearby surface
waters (Birgand 2000; Stewart and Reneau 1984), and the distance from the source to the
receiving surface waters (Stacey 2002). One study from the U.K. (Hiscock et al. 1991) estimates
that average groundwater carbon content would account for removal of 3 mg/L of nitrate.
3.3 Phosphorus Approximately 20 to 30 percent of the P in wastewater is removed in septic tanks (Lombardo
2006). P removal in soil effluent dispersal systems is achieved primarily by mineral precipitation.
The process involves sorption and complex biogeochemical mechanisms that rely on dissolved
P mineralization with iron, calcium, and aluminum (Tyler et al. 2003; Stone Environmental 2005;
Lombardo 2006). The stability of those processes is influenced by pH, redoximorphic conditions,
and the chemistry of aluminum and iron. The soil’s capacity to remove P is significant both
spatially and temporally. Sorption can be reversible—as with sands, or relatively permanent, as
in soils high in iron oxides.
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In general, most regions of the Chesapeake Bay watershed have soils that retain high levels of
P from decentralized systems. Areas where soil-based, P-removal rates are low include highly
permeable soils, such as sands, loamy sands, and soils very high in gravel. In areas with
sufficient soil P-removal capacity, saturation fronts of P move only inches or less per year.
Wastewater system designers maximize P-removal rates by locating the infiltration system in
medium- to fine-textured soils that are as far from surface waters as possible, and extending the
infiltration system along the topographic contour of the installation site. Also, uniform dosing and
resting dispersal by pressure or drip distribution will optimize P removal in the soil by increasing
the contact time between the effluent and the soil.
If native soils are not amenable to adsorption removal, other adsorption methods are available
(Stone Environmental 2005; Dimick et al. 2006; USEPA 2002a). Although some P can be
removed by pretreatment systems that contain high concentrations of adsorptive elements or by
biological P removal, soil adsorption is by far the most common and least expensive means of
removal. Where soils are inadequate for P removal, mound systems that use more appropriate
soil (possibly imported) might be required. System use over time slowly reduces the capacity of
the soil to remove P.
3.4 Permeable Reactive Barriers Specific types of PRBs have been developed to remove nitrate from groundwater plumes that
would otherwise adversely affect surface water quality. PRBs consist of a trench filled with a
degradable carbon source (e.g., sawdust, newspaper) and are sited to intercept high-nitrate
groundwater plumes (WE&T 2009) before they enter surface waters (Figure 6-1). As the plumes
pass through the low-oxygen,
carbon-rich barrier, bacteria
break down nitrate molecules to
use the oxygen for cell
respiration. In areas where
receiving waters are already
eutrophied, the trenches
provide immediate relief by
removing nitrate from the
incoming groundwater.
Addressing the source of the
high-nitrate plume (i.e., densely
sited septic systems) would
also produce results, but any
measureable effects would
likely take several years
Source: USEPA 1998
Figure 6-1. PRB conceptual approach.
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because of slow effluent plume movement in most soils and could be more expensive and
require more maintenance than installing PRBs.
PRBs are typically installed as long, narrow trenches perpendicular to the incoming plume and
parallel to the shoreline. The most effective ones for removing nitrate from plumes are filled with
a carbon-based media mix that controls for changes in pH. Such systems have been
successfully demonstrated in North America and Europe (Vallino and Foreman 2008; Robertson
and Cherry 1995; Lombardo et al. 2005; USEPA 1998). Costs range from about $5,000 to
$15,000 per equivalent dwelling unit (i.e., in the plume sourcing area), depending on soils,
geology, depth to groundwater, subsurface hydrology, construction access, existing
infrastructure, and other factors. Zero valent iron, now used for some industrial wastewater
treatment applications, has been studied as a nutrient-removal media in PRBs and other system
components. Obstacles with this technology include reduction of nitrate to ammonia rather than
N gas and relatively high costs (Cheng 1997). New variations of this technology hold promise
for removing some of these obstacles (Lee et al. 2007).
3.5 System Configuration As noted above, a certain level of treatment process sophistication and soil discharge technique
(e.g., pressure dosing, drip dispersal) are required for optimum N removal. Their cost in terms of
both hardware and management needs can be significantly mitigated through the use of cluster
systems that treat wastewater from multiple homes or businesses. Cluster systems, also called
community or distributed systems, have become extremely popular in areas where high levels
of wastewater treatment are required, where space is too limited for on-site conventional soil-
discharging systems, and local funding capacity precludes conventional sewage collection and
treatment (see Section 4.6).
It should be noted that soil-discharging wastewater systems that have the capacity to serve 20
or more people per day are defined by EPA as Class 5 underground injection wells and are
therefore subject to permitting and other requirements for large-capacity septic systems under
the federal Safe Drinking Water Act. Further, any decentralized system that accepts waste other
than sanitary wastewater (such as industrial waste) is an Underground Injection Control (UIC)
Class 5 Injection Well. UIC regulatory information for large-capacity septic systems is posted at
http://www.epa.gov/safewater/uic/class5/types_lg_capacity_septic.html.
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4 Treatment Technologies and Costs Key considerations in treatment system selection are wastewater flow, strength (i.e.,
biochemical oxygen demand), the presence of nonconventional organic or inorganic
constituents, the sensitivity of the receiving environment, and the capacity of system managers
to operate and maintain it over the long term. Given those factors, both the selection and
ongoing use of a specific technology is driven by management considerations. For example,
wastewater characterization and assessment of the receiving environment are planning-level
activities that result in establishing performance standards, which begin to identify the narrow
range of treatment technology options and related design considerations. Once a specific
system is selected, construction oversight, operation, inspection, maintenance, and residuals
removal—all management program elements—become paramount in ensuring perpetual
performance.
The La Pine Decentralized Wastewater Demonstration Project (Rich 2005) has provided some
of the most comprehensive field data on the performance of various system types. The
project—funded by EPA and supported by the Deschutes County, Oregon, Environmental
Health Division; Oregon Department of Environmental Quality; and the U.S. Geological
Survey—monitored system performance between 1999 and 2005 (see Figure 6-2 and
Table 6-1). System performance was found to be affected by a number of variables, but in
general the level of analysis provides insight on the range of pollutant removal that can be
expected from the various system types. The figure and table that follow summarize key data
from the project; detailed performance results, system descriptions, and other information are
available in the final project report (Rich 2005).
The subsections that follow discuss the main classes of treatment system technologies. The
final section of this chapter summarizes management program elements that support the
implementation measures provided at the beginning of this chapter. Table 6-2 provides
examples of biological N-removal performance from the literature for a variety of technologies.
Table 6-3 contains details on specific treatment systems described in the subsections below.
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Source: Rich 2005.
Figure 6-2. Effluent TN concentrations for systems tested in the La Pine Project.
Table 6-1. System components and type classifications for Figure 6-2
System component/type General classification
Septic Tank Primary treatment vessel
Lined Sand Filter Attached growth, sand media
Bottomless Sand Filter Attached growth, sand media
AdvanTex AX-20 Attached growth, textile media
AdvanTex RX-30 Attached growth, textile media
Puraflo Attached growth, peat media
Dyno2 Attached growth, gravel media, wetland polishing
Amphidrome Attached growth/suspended growth hybrid
Biokreisel Attached growth/suspended growth hybrid
EnviroServer Attached growth/suspended growth hybrid
FAST Bio-Microbics Attached growth/suspended growth hybrid
IDEA Suspended growth
Nayadic Suspended growth
NiteLess Suspended growth with add-on anoxic filter
NITREX Add-on anoxic filter
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4.1 Conventional Systems Conventional treatment systems featuring septic tanks and soil infiltration systems are the most
commonly used wastewater treatment technologies. The soil dispersal system facilitates aerobic
treatment, degradation, filtration, and adsorption of contaminants not treated or retained by the
septic tank. However, N removal is somewhat limited, with TN concentrations before soil
application typically in the 40–50 mg/L range. In sandy soils with little organic content, high
oxygen levels, and poor downgradient mixing, N concentrations can remain high even after
several hundred feet of effluent plume movement (Walker et al. 1973; Robertson and Cherry
1992; Cogger 1988; Joubert et al. 2003). Given the low N-removal rates of conventional
systems (i.e., averaging 20 percent TN removal; Otis 2007; Smith et al. 2008; Jenssen and
Siegrist 1990), they are no longer appropriate for use in new communities or densely developed
areas in the Chesapeake Bay watershed.
4.2 Land/Vegetative Treatment Systems Land treatment systems, such as spray irrigation systems, are permitted in some places but
have not been widely used because of their large land area requirements (USEPA 2000). In
general, such vegetative treatment systems have shown poor performance with regard to N
removal. However, in recent years, significant advances have been made. The Living Machine,
a proprietary decentralized wastewater treatment system has been used successfully for large-
capacity applications, such as schools. While the system delivers advanced N removal, it relies
on multiple treatment processes including anaerobic and aerobic reactors, a clarifier, and an
ecological fluidizer bed (USEPA 2002b), which drive up the cost. Eco-machines are similar in
concept to The Living Machine and are capable of advanced N removal. Costs for both of these
technologies make sense for only fairly large-capacity applications. They are not practical for
individual residential systems but could be useful for cluster and large system applications.
4.3 Suspended Growth Systems Suspended growth systems, such as activated sludge-based aerobic treatment units (ATUs),
are generally effective in nitrifying septic tank effluent. Denitrification is somewhat limited but
can be aided by process controls (e.g., recirculation) and effluent dispersal via time-dosing into
the upper soil horizon (Stewart 1988). Aerobic units that feature aeration that periodically stops
and starts show improved denitrification. Sequencing batch reactors, which first fill and then
draw, in alternating aerobic/anoxic cycles in a single tank might also meet the 20 mg/L
recommended effluent limit for areas more than 1,000 feet from surface waters in the
Chesapeake Bay watershed, when effluent is dispersed to the soil via time-dosed pressure
application (Washington State Department of Health 2005). Capital costs for conventional
on-site suspended growth systems range from $7,500 to $15,000 per equivalent dwelling unit
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(EDU), with O&M expenses of $400 to $800 per EDU per year when all suggested O&M tasks
are performed (Tetra Tech 2007).
N removal in larger cluster applications of suspended growth systems (i.e., > 200 homes) can
be enhanced by incorporating a membrane bioreactor process (MBR) unit, which screens
wastewater through very small pore-size filters. MBRs are more common to centralized
treatment facilities because of operating costs and economy of scale issues. However,
individual home-sized and small cluster units are beginning to be developed for the U.S. market
(e.g., BioBarrier, ZeeWeed; WERF 2006). The high-quality effluent provides opportunities for
treated water reuse. Cost and performance data for individual and small cluster applications of
MBRs are not widely available and are likely to vary greatly. Energy costs, particularly to
operate the pumping components, are often significant, especially in smaller system
applications (USEPA 2007).
4.4 Attached Growth Aerobic Systems These systems (sometimes called trickling filters or media filters) use natural aeration instead of
mechanical, produce less sludge for disposal, and require less power and O&M than the
suspended growth units in performing the same tasks. All the systems listed in Table 6-3 are
varieties of attached growth system types. Like suspended growth systems, attached growth
treatment units also require a recirculation step to meet more stringent TN-removal objectives.
Commercially available systems come in lightweight packages and employ lightweight media for
easy installation. They also require about 20 percent less physical footprint than typical trickling
filters. When properly loaded and operated, they can produce very high nitrification levels that
must be followed by a denitrification step to exceed the typical 50 percent N-removal rate.
Attached growth systems are also often quite stable compared with suspended growth
processes, which might be important, particularly for decentralized systems serving periodically
or seasonally used facilities. On-site capital costs are slightly higher in general than the
suspended growth ATUs ($10,000–$16,000 per EDU), but O&M costs are significantly less,
e.g., about $200–$300 per EDU per year (USEPA 2010; Tetra Tech 2007).
N removal in attached growth media filters can be optimized through internal treatment system
process controls. Single-pass media filters—sand filters, textile filters, peat systems, mounds,
and other packed media bed units—achieve excellent nitrification levels but generally do a poor
job with denitrification unless some, or all, of the effluent passes through a carbon-rich, low-
oxygen environment after the nitrification stage. That can be accomplished by recirculating a
portion of the effluent back to the septic tank or a pump tank, or by adding a denitrification unit
to the system, or both. Media filters have a long record of excellent performance, with
nitrification rates as high as 95 percent (Otis 2007; Smith et al. 2008; USEPA 2002a). The
treatment process is stable year-round and can be employed through either custom-built,
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nonproprietary engineered systems or commercial units that can be installed in a single day.
Capital costs for single-pass filters range from $5,500 to $13,000 per EDU, with O&M expenses
of $200 to $400 per EDU per year (USEPA 2010; Tetra Tech 2007).
Recirculating media filters have been in use for many years and feature high nitrification rates
with about 50–70 percent TN reduction. The systems recycle part of the effluent back to the
septic tank or the recirculating tank, where the anoxic environment and available carbon
facilitate denitrification processes. Design considerations include the ratio of effluent recirculated
and the configuration of the recycle plumbing, i.e., ensuring that the recycled effluent is
discharged to a tank location with low oxygen and some carbon. TN effluent concentrations can
be as low as 10 mg/L, which can be further reduced in the soil by using time-dosed, pressure-
drip effluent dispersal. Engineered systems and proprietary units are widely available and can
serve single homes or large subdivisions. Capital costs for recirculating systems range from
$9,500 to $20,000 per EDU, with O&M expenses of $350 to $600 per EDU per year (USEPA
2010; Tetra Tech 2007; Washington State Department of Health 2005).
4.5 Add-On Anoxic Filters with a Carbon Source Optimal denitrification can be achieved by passing nitrified effluent through a low-oxygen,
carbon-rich environment before soil dispersal. Engineered and proprietary systems featuring
add-on anoxic filters with an external carbon source (e.g., methanol, sawdust, newspapers)
have performed successfully in single-home and cluster applications. For example, at least one
commercially available product (NITREX) regularly produces effluent with N concentrations of
less than 5 mg/L (Heufelder et al. 2007, see also Figure 6-2 and Table 6-2). Others claim to
have similar systems with comparable performance, although, to date, independent field
verification is lacking. NITREX relies on a passive nitrate remediation biofilter unit that uses a
processed wood by-product as the filter medium. Other system designs discussed above can
approach that level when paired with time-dosed, shallow pressurized dispersal. Capital costs
for add-on denitrification systems range from $3,500 to $7,000 and more per EDU, with O&M
expenses of less than $100 per year (Washington State Department of Health 2005). Note that
those are added costs and do not include costs for the septic tank, nitrification process unit, or
soil dispersal system—just the add-on component.
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Table 6-2. Examples of biological N removal performance from the literature
Technology examples TN removal efficiency
(%) Effluent TN
(mg/L)
Suspended growth
Aerobic units w/ pulse aeration 25%–61%a 37–60a
Sequencing batch reactor 60%b 15.5b
Attached growth
Single-Pass Sand Filters (SPSF) 8%–50%c 30–60c
Recirculating Sand/Gravel Filters (RSF) 15%–84%d 10–47d
Multi-Pass Textile Filters (AdvanTex AX20) 64%–70%e 3–55e
RSF w/ Anoxic Filter 40%–90%f 7–23f
RSF w/ Anoxic Filter & external carbon source 74%–80%g 10–13g
RUCK system 29%–54%h 18–53h
NITREX 96%i 2.2i
Source: Adapted from Washington Department of Health 2005
Notes: Overall performance can vary, depending on system configuration and other factors. For detailed descriptions of treatment processes and technologies, see http://www.psparchives.com/publications/our_work/hood_canal/hood_canal/n_reducing_technologies.pdf.
a. California Regional Water Quality Control Board 1997; Whitmeyer et al. 1991
b. Ayres Associates 1998
c. Converse 1999; Gold et al. 1992; Loomis et al. 2001; Nolte & Associates 1992; Ronayne et al. 1982
d. California Regional Water Quality Control Board 1997; Gold et al. 1992; Loomis et al 2001; Nolte & Associates 1992; Oakley et al. 1999; Piluk and Peters 1994; Ronayne et al. 1982
e. NSF International 2009
f. Ayres Associates 1998; Sandy et al. 1988
g. Gold et al. 1989
h. Brooks 1996; Gold et al. 1989
j. Rich et al. 2003
4.6 Composting Toilet Systems Composting toilet systems that contain and treat toilet wastes can reduce watershed N
discharges significantly, because such wastes account for 70–80 percent of the TN load in
domestic wastewater. Composting systems have been used successfully in both private and
public facility settings. Like all systems, they require appropriate design and ongoing
maintenance. A graywater treatment system is needed if the facility generates sink, laundry, or
other graywater, therefore adding to the cost. Capital costs for composting systems (and
excluding the cost of graywater systems) range from $2,500 to $10,000, with O&M expenses of
$50 to $100 per year (USEPA 1999). The single-house viability of such systems depends on
local codes and the owner’s attitude, though acceptance and use of composting systems is
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increasing because of improved designs, performance, and lower maintenance requirements.
The systems are more frequently used in public settings, such as parks and campgrounds.
4.7 Cluster Treatment Systems Generally, cluster systems collect wastewater from multiple houses through low-cost sewerage
and treat and disperse the effluent to soil-based dispersal systems similar to on-site systems.
Many homes and businesses can be served by a single treatment facility. Most cluster systems
feature septic tanks on each building lot; collection piping that operates via gravity, vacuum, or
pressure; a treatment facility with attached growth process units; and a soils-based dispersal
field for the effluent. Add-on anoxic denitrification filters can be included. Effluent is typically
dispersed to the soil under pressure (e.g., pressure, drip, time or demand dosing) to assure
uniform application throughout the larger drainfield. Collection technologies include grinder
pump systems, which macerate and transport all sewage; effluent sewers, such as the septic
tank effluent pump (STEP); the septic tank effluent gravity (STEG) collection system; and
vacuum systems.
Advanced treatment systems can facilitate local reuse of the treated effluent for toilet flushing,
irrigation, industrial purposes, or just be used to replenish aquifers. The cost of a cluster
collection system varies significantly according to the number of users, collection system
logistics, treatment facility design, land availability, materials, labor costs, and other factors.
Cluster systems can achieve economies of scale to provide high levels of treatment at costs
significantly less than individual systems and centralized sewer systems. New cluster systems
generally range from $10,000 to $18,000 per EDU in non-urbanized areas of new development,
with higher costs for retrofits in urban areas, depending on the treatment technology used
(USEPA 2010; Tetra Tech 2007). Replacement and retrofit systems have similar costs, but
collection system installation can drive costs higher. An RME with the technical, financial, and
managerial capacity to ensure viable, long-term, cost-effective performance is essential for
cluster system applications. Total system annual O&M costs range from $450 to $750 per EDU
per year (Tetra Tech 2007).
4.8 Soil Dispersal Systems Gravity-based, soil dispersal systems generally include conventional perforated pipe, laid in
stone-filled trenches or purchased with Styrofoam beads surrounding the pipe and wrapped in
netting; and gravelless, open-bottomed leaching chambers. N removal in the soil increases
when effluent is dispersed in a time-dosed manner (i.e., dose/rest cycle) in the uppermost soil
horizon (i.e., within one foot of the ground surface). Time-dosed, pressure-drip dispersal in the
top 12 inches of soil has been credited with a 50 percent reduction in Tennessee (Long 1995),
making the option an important feature for achieving the performance standards recommended
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in this chapter. As in all effluent dispersal systems, maximizing the separation distance between
effluent application and restrictive soil boundaries (e.g., hardpan, bedrock, perched water
tables, seasonal high water tables) improves performance.
Another effluent-dispersal strategy that improves performance is the use of alternating soil
dispersal fields. Most conventional systems continuously load drainfields with effluent, resulting
in a gradual reduction of the soil’s capacity to treat effluent over time. Alternating drainfields that
are used for 6 months then rested for 6 months improves the performance of the soil dispersal
system and should be favored over conventional drainfields. Such systems require relatively low
additional investment and can greatly extend the life of the soil dispersal system (Noah 2006).
Maintenance programs for such systems should be designed and implemented in concert with
the local health department or RME to ensure that flow-diversion devices are operated on
schedule. Because this strategy applies to conventional septic drainfields, this recommendation
applies primarily to areas of new development outside sensitive areas and subdivisions.
4.9 Effluent Reuse Reusing treated wastewater system effluent can significantly reduce N discharge to the
environment. Many of the technologies suggested for advanced decentralized wastewater
treatment in the Chesapeake Bay watershed can, with adaptations, be used to produce
reclaimed water for beneficial reuses, including aquifer recharge, landscape irrigation, toilet
flushing, fire protection, cooling and other nonpotable indoor and outdoor purposes (USEPA
2004). When reclaimed water is used for irrigation, reuse can offset potable water demand by
augmenting supply while sequestering nutrients in vegetative matter and offsetting fertilizer use
(WERF 2010). Reclaimed water technologies generally include recirculating filtration systems
and membrane bioreactors, amended with disinfection systems (most commonly, chlorination or
ultraviolet disinfection or both), online monitoring systems, on-site storage, and sometimes
specific chemical feed systems for conditioning treated effluent to meet water quality demands
for specific reuses (e.g., pH adjustment for cooling water). Nonreactive dye injection is
sometimes required by building codes for reclaimed water to be used indoors. Costs for
decentralized reclaimed water systems are highly context-specific and dependent on the
intended reuse application, system size, and local or state regulatory requirements (WERF
2010) but can be assumed to add 50 percent to the costs of a more traditional decentralized
system.
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Table 6-3. Products that have completed the EPA ETV process for N reduction in domestic wastewater from individual homes, as of May 2005
System name Technology Description of process Performance Cost
Waterloo Biofilter® Model 4-Bedroom Waterloo Biofilter Systems, Inc. 143 Dennis St.: P.O. Box 100 Rockwood, Ontario Canada N0B 2K0
http://www.nsf.org/business/water_quality_protection_center/pdf/Waterloo-VS-SIGNED.pdf
Fixed film trickling filter.
The biofilter unit uses patented lightweight open-cell foam that provides a large surface area. Settled wastewater from a primary septic tank is applied to the surface of the biofilter with a spray distribution system. The system can be set up using a single pass process (without any recirculation of biofilter treated effluent) or can use multi-pass configurations. The ETV testing results were generated by returning 50% of the biofilter effluent back to the primary compartment of the septic tank.
It averaged 62% removal of TN with an average TN effluent of 14 mg/L over the 13-month testing period. Earlier testing of this product in a single pass mode demonstrated that it could produce a 20–40% TN reduction.
$13,000–$17,000 for total system installation. The Waterloo Biofilter unit only would cost approximately $7,000.
Amphidrome™ Model Single Family System
F.R. Mahony & Associates, Inc. 273 Weymouth St. Rockland, MA 02370
http://www.nsf.org/business/water_quality_protection_center/pdf/Amphidrome_VS.pdf
Submerged growth sequencing batch reactor (SBR) in conjunction with an anoxic/equalization tank and a clear well tank for wastewater treatment
The bioreactor consists of a deep bed sand filter, which alternates between aerobic and anoxic treatment. The reactor operates similar to a biological aerated filter, except that the reactor switches between aerobic to anoxic conditions during sequential cycling of the unit. Air, supplied by a blower, is introduced at the bottom of the filter to enhance oxygen transfer.
It averaged 59% removal of TN effluent of 15 mg/L over the 13-month testing period at the Massachusetts Alternative Septic System Test Center (MASSTC).
$7,500 for unit only. The manufacturer estimates it would cost $12,000–$15,000 for a complete installation.
SeptiTech® Model 400 System SeptiTech, Inc. 220 Lewiston Road Gray, ME 04039
http://www.nsf.org/business/water_quality_protection_center/pdf/SeptiTech_VS.pdf
Two-stage fixed film trickling filter using a patented highly permeable hydrophobic media
Clarified septic tank effluent flows by gravity into the recirculation chamber of the SeptiTech unit. A submerged pump periodically sprays wastewater onto the attached growth process and the wastewater percolates through the patented packing material. Treated wastewater flows back into the recirculation chamber to mix with the contents. Treated water flows into a clarification chamber and is periodically discharged to disposal unit (drainfield, drip irrigation, etc.)
Averaged 64% removal of TN with an average TN effluent of 14 mg/L over the 12-month testing period at MASSTC.
$11,000 for SeptiTech unit includes shipping and installation. The manufacturer estimated that a total system with pressure distribution drainfield would cost approximately $20,000.
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Table 6-3. Products that have completed the EPA ETV process for N reduction in domestic wastewater from individual homes, as of May 2005 (continued) System name Technology Description of process Performance Cost
Bioclere™ Model 16/12 Aquapoint, Inc. 241 Duchanine Blvd. New Bedford, MA 02745
http://www.nsf.org/business/water_quality_protection_center/pdf/Bioclere-VS-SIGNED.pdf
Fixed film trickling filter.
Septic tank effluent flows by gravity to the Bioclere clarifier unit from which it is sprayed or splashed onto the fixed film media. Treated effluent and sloughed biomass are returned to the clarifier unit. A recirculation pump in the clarifier periodically returns biomass to the primary tank. Oxygen is provided to the fixed film by a fan located on the top of the unit.
Averaged 57% removal of TN with an average TN effluent of 16 mg/L over the 13-month testing period at MASSTC.
$7,500 for unit itself. Price for total system would need to include primary septic tank, Bioclere unit and disposal option, with costs in the range of $12,000–$15,000. The manufacturer recommends use in clusters to reduce per home costs and facilitate maintenance. Experience with a 27-home cluster resulted in costs of $6,800– $8,000 per home.
Retrofast 0.375 System Bio-Microbics 8450 Cole Parkway Shawnee, KS 66227
http://www.nsf.org/business/water_quality_protection_center/pdf/Biomicrobics-FinalVerificationStatement.pdf
Submerged attached-growth treatment system, which is inserted as a retrofit device into the outlet side of new or existing septic tanks.
The RetroFAST 0.375 System is inserted into the second compartment of the septic tank. Air is supplied to the fixed film honeycombed media of the unit by a remote blower. Alternate modes of operation include recirculation of nitrified wastewater to the primary settling chamber for denitrification. Intermittent use of the blower can also be programmed to reduce electricity use and to increase nitrification.
Averaged 51% removal of TN with an average TN effluent of 19 mg/L over the 13-month testing period at MASSTC.
Product and installation cost for the Retrofast 0.375 System ranges is estimated to be $4,000–$5,500 depending on existing tankage. That cost includes the FAST unit, blower, blower housing and control panel. The local representative for Bio-Microbics units believes costs could be as low as $3,500 for multiple units.
Recip® RTS-500 System Bioconcepts, Inc. P.O. Box 885 Oriental, NC 28571-0885
http://www.nsf.org/business/water_quality_protection_center/pdf/Bioconcepts_Verification_Statement.pdf
Fixed film filter
This is the newest product to complete ETV Program testing. It is a patented process developed by the Tennessee Valley Authority (TVA) and uses a fixed film filter medium contained in two adjacent, equally dimensioned cells. Timers on each of the two reciprocating pumps control the process.
Averaged 58% removal of TN with an average TN effluent of 15 mg/L over the 12-month testing period at MASSTC.
Very limited experience with this single-family unit. The unit built for ETV testing was a prototype. The cost per unit, by itself, is estimated to be $8,000–$10,000. Cost of the septic tank and disposal unit would be extra and the cost would depend on site conditions. Conservatively, cost for a total system could be $11,000–$15,000.
Source: Adapted from Washington Department of Health 2005
Guidance for Federal Land Management in the Chesapeake Bay Watershed
5 Wastewater Planning and Treatment System Management
The previous section describes N-removing individual or cluster wastewater system
technologies, system configurations, and effluent dispersal options. This section describes
management considerations that are essential for optimizing treatment system selection, sizing,
performance, and long-term use, such as inventory systems, wastewater planning, performance
standards, siting and installation guidelines, operation, inspection, maintenance, and residuals
handling. The management tasks described in this section are paramount for reducing nutrient
inputs to the Chesapeake Bay because they establish the framework for selecting and using
specific treatment systems in particular locations. For example, advanced cluster systems are
the best approach for protecting and restoring the Chesapeake Bay when considering
wastewater facilities for new subdivisions and replacing significant numbers of malfunctioning
systems in existing subdivisions.
The following subsections summarize key management program elements viewed as important
for controlling the input of nutrients and other pollutants to the Chesapeake Bay. EPA has
provided extensive guidance, case studies, resources, references, and links on these
management program topics (USEPA 2005, 2010). Specific, detailed information on each topic
below is provided in EPA’s (2005) Handbook for Managing Onsite and Clustered (Decentralized)
Wastewater Treatment Systems, available online at
http://cfpub.epa.gov/owm/septic/septic.cfm?page_id=289.
5.1 Public Education and Involvement Decentralized wastewater management programs require public support. The success of such
programs will depend on how well homeowners, system service providers, and other
stakeholders are involved in the development process. Unless people understand the need for a
management program, there is little chance it will be adopted. Once in operation, the program
must keep the community engaged, involved, and informed. Managers should give special
consideration to explaining the need for new requirements for system upgrades, inspections, or
other performance measures.
EPA has partnered with a variety of nonprofit organizations involved in decentralized
wastewater management to improve public education, outreach, and involvement through
development of informational materials, technical products, and training programs. Links to
these partner organizations and the educational, technical, and other resources they provide are
provided at http://cfpub.epa.gov/owm/septic/septic.cfm?page_id=260. EPA maintains a
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repository of print, radio, and TV public service announcements and other materials specifically
pertaining to septic system education in its Nonpoint Source Outreach Toolbox, online at
http://www.epa.gov/nps/toolbox/.
5.2 Planning Planning can be used to integrate management strategies for areas served by both centralized
and decentralized wastewater treatment facilities, serve as the basis for ordinances and
subdivision regulations, and synchronize the community growth plan in harmony with the water
and wastewater infrastructure investments. Integrating wastewater planning functions provides
better long-term management of facilities and can help local officials deal with a number of
needs such as sewer overflows, National Pollutant Discharge Elimination System effluent
limitations, total maximum daily loads (TMDLs), and antidegradation requirements. For
example, integrated planning can minimize problems associated with competition for infiltration
areas between wastewater and stormwater management facilities in new developments, and is
useful in anticipating and preventing adverse water quality effects. Variables to consider during
the planning process include wastewater flows, proximity and uses of nearby water resources,
landscape topography, hydrology, hydrogeology, soils, environmentally sensitive areas,
infrastructure system options and locations, population densities, and need and potential for
clustering treatment or reuse facilities.
EPA supports a wide range of water resource planning and management functions through
programs such as the Clean Water Act section 319 nonpoint source management program, the
Clean Water Act 305(b) assessment reports, TMDLs, wellhead and source water protection
programs, watershed planning initiatives, coastal management, National Estuary Program,
wetlands protection programs, water quality standards, continuous planning processes under
section 303(e), water quality management processes under section 205(j) and 604(b), the Clean
Water State Revolving Fund, and so on. Ideally, the planning and management activities
supporting decentralized wastewater treatment would be integrated, or at least coordinated, with
these and other water resource programs, many of which the states operate.
5.3 Performance Requirements Performance requirements for systems are necessary to minimize the risks they pose to health
and water resources. Performance requirements specify objectives for each wastewater
management system, which can include physical, chemical, and biological process
components. Performance compliance is based on pollutant-removal estimates for the various
system components (e.g., septic tank, suspended-growth or fixed-film reactors, lagoons,
wetlands, soil, disinfection), verified by periodic field inspections and sampling. Performance
can be measured via numeric or narrative criteria. Numeric criteria reflect time-based, mass
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loadings or pollutant-concentration limits designed to protect sensitive water resources.
Pollutants commonly targeted in performance requirements include nutrients, bacteria, oxygen
demand, and solids.
5.4 Recordkeeping, Inventories, and Reporting System inventories provide the nuts and bolts for on-site management. Basic system
information—location, type, design capacity, owner, installation, and servicing dates—is
essential to an effective program. The best record-keeping programs feature integrated
electronic databases with field unit data entry (i.e., using a handheld personal digital assistant),
save-to-file computer assisted design drawings, user-specified reporting formats, and GIS-
based spatial data management and user interface systems.
5.5 Financial Assistance and Funding Financial assistance might be needed to (1) develop or enhance a management program;
(2) provide support for constructing and modifying wastewater facilities; and (3) support
operation of the program. Funding for program development and operation is often available
from public and private loan or grant sources, supplemented by local matching funds. It can also
be derived from some form of resource sharing among management program partner
organizations such as planning departments or health and water resource agencies. Developing
an RME and financing for constructing and operating facilities require larger investments that
might come from grants and loans or public-private partnerships. Long-term operating costs are
usually borne by system users through payment of fees and assessments.
5.6 Site Evaluation Evaluating a proposed site in terms of its environmental conditions, physical features, and soil
characteristics provides the information needed to size, select, and locate an appropriate
wastewater treatment system. Regulatory authorities issue installation permits on the basis of
the information collected and analyses performed during the site evaluation. Prescriptive site
evaluation, design, and construction requirements are based on experience with conventional
septic tank/soil dispersal systems and empirical relationships that have evolved over the years.
A soil analysis to a depth of 4 to 6 feet using a hand auger, drill rig, or a backhoe pit, rather than
a simple percolation test, provides a better approach for assessing soils, seasonal water table
fluctuations, and other subsurface site features. Performance-based approaches require a more
comprehensive site evaluation. Site evaluation protocols can include some presently employed
empirical tests, specific soil properties tests, and soil pits to characterize soil horizons, mottling,
and a variety of other properties. Modeling groundwater and surface water impacts of multiple
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systems in defined areas (e.g., stream subwatershed) can help to further refine performance
requirements and related system site and design considerations.
5.7 System Design Decentralized wastewater treatment system design requirements focus on protecting public
health and water resources. However, systems should also be affordable and aesthetically
acceptable. Prescriptive codes that specify standard designs for sites meeting minimum criteria
simplify design reviews, but they limit development options and the potential for efficiently
meeting performance requirements. Where management programs rely on the state code for
design, there might not be any need for special review procedures for alternative system
designs. However, in sensitive environments where performance codes are employed, there is
a need to include allowances for alternative designs even if they only expand the number of
prescriptive system choices and site parameters for sites that do not meet the conditions for
conventional systems. Design considerations should address the potential implications of water
conservation fixtures, effects of different pretreatment levels on hydraulic and treatment
performance of soil-based systems, and the O&M requirements of different pretreatment and
soil dispersal technologies.
5.8 Construction/Installation Poor installation can adversely affect performance of both conventional and advanced systems
that rely on soil dispersion and treatment. Most jurisdictions allow installation or construction to
begin after issuance of a construction permit, which occurs after the design and site evaluation
reports have been reviewed and approved. Performance problems linked to installation/
construction are typically related to soil wetness during construction, operation of heavy
equipment on soil infiltration areas, use of unapproved construction materials (e.g., unwashed
aggregate containing clay or other fines), and overall construction practices (e.g., altering trench
depth, slope, length, location). The effects of improperly installed soil-based systems generally
occur within the first year of operation in the form of wastewater backups. Some improper
construction practices might not be as evident and could take years to manifest themselves in
the form of degraded groundwater or surface water. The regulatory authority or other approved
professionals should conduct inspections at several stages during the system installation
process to ensure compliance with design and regulatory requirements.
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5.9 Operation and Maintenance O&M is important for all wastewater treatment systems, especially those that rely on
components that are difficult to remedy if damaged—such as a soil dispersal system. Most
system user information includes building awareness of inputs that might affect treatment
processes, such as strong cleaners, lye, acids, biocides, paint wastes, oil and grease, and the
like. Gravity-flow, soil-infiltration systems require little O&M beyond limiting inputs to normal
residential wastes, cleaning effluent screens/filters, and periodic tank pumping (e.g., every 3 to
7 years). Systems employing advanced treatment technologies and electromechanical
components require more intensive O&M attention, e.g., checking switches and pumps,
measuring and managing sludge levels (important for all systems), monitoring and adjusting
treatment process and system timers, checking effluent filters, monitoring effluent quality, and
maintaining disinfection equipment. Operators and service technicians should be trained and
certified for the types of systems they will be servicing; services should be logged and reported
into a management tracking system, such as EPA’s TWIST (USEPA 2006), so that long-term
performance can be tracked. The use of a dial-up modem or Internet-based monitoring
equipment can improve operator efficiency and performance tracking when large numbers of
systems are involved.
5.10 Residuals Management Septic tanks contain settleable solids, fats, oils, grease, and other residuals that require periodic
removal. The primary objective for septage management is to establish procedures for handling
and dispersing the material in a manner that protects public health and water resources and
complies with applicable laws. Approximately 67 percent of the estimated 12.4 billion gallons of
septage produced annually in the United States is hauled to publicly owned treatment works or
other facilities for treatment, while the remaining 33 percent is applied to land. Federal
regulations (under Title 40 of the Code of Federal Regulations Part 503) and state/local codes
strive to minimize exposure of humans, animals, and the environment to chemical contaminants
and pathogens that are often present in septage. Residuals management programs should
include tracking or manifest systems that identify sources, pumpers, transport equipment, final
destination, and treatment or management techniques.
5.11 Training and Certification/Licensing A variety of professionals and technicians including planners, regulators, designers, installers,
operators, pumpers, and inspectors, are all involved in some aspect of a decentralized
wastewater management program. Training, along with certification or registration, provides
system owners and users with competent service providers and promotes professionalism
among the industry. Service providers need to have a solid working knowledge of treatment
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processes, system components, performance options, O&M requirements, and
laws/regulations. Universities, colleges, technical schools, agency-sponsored training programs,
regional/local workshops, or formal/informal apprenticeship programs can provide such training.
Service providers should have extensive and detailed knowledge of their own service areas and
a general grasp of other related activities (e.g., planning or site evaluation). Service providers
should pursue opportunities for cross-training, joint accreditation/certification, and sharing of
training resources wherever possible.
5.12 Inspections and Monitoring Perhaps the most significant shortcoming in existing management programs is the lack of
regular inspections and performance monitoring. Area-wide monitoring regimes include testing
groundwater and surface waters for indicators of substandard treatment, such as the presence
of human fecal bacteria and excess nutrients. All systems need to be inspected, at an interval
defined by the technological complexity of system components, the receiving environment, and
the relative risk posed to public health and valued water resources. The best approach is to
establish an inspection regime and schedule on the basis of the system’s relative reliance on
electromechanical components combined with health and environmental risk. Less effective
surrogate approaches include, in order of descending effectiveness (1) requiring comprehensive
inspections at regular intervals; (2) third-party inspections at the time of property transfer;
(3) inspections only as part of complaint investigations.
5.13 Corrective Actions and Enforcement A decentralized wastewater management program should be enforceable to assure compliance
with laws and to protect public health and the environment. Management agencies should have
the legal authority to adopt rules and assure compliance by levying fines, fees, assessments, or
by requiring service providers to respond to system malfunctions. Program administrators
should emphasize those tools that encourage compliance, rather than punishment. It also helps
to have the support of the courts to implement an effective enforcement program. To assure
compliance, management agencies typically need authority to do the following:
Respond promptly to complaints
Issue civil and criminal actions or injunctions
Provide meaningful performance inspections
Condemn systems or property
Issue notices of violation (NOVs)
Correct system malfunctions
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Implement consent orders and court orders
Restrict real estate transactions
Hold formal and informal hearings
Issue fines and penalties
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